JP3705722B2 - Surface wave device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an end surface reflection type surface acoustic wave device using an SH type surface acoustic wave.
[0002]
[Prior art]
Conventionally, an end surface reflection type surface wave device using an SH type surface wave is known. The SH type surface wave is a surface wave whose main component is a component whose displacement is perpendicular to the surface wave propagation direction and parallel to the substrate surface, such as a BGS wave or a Love wave. As such an end surface reflection type surface wave device, in order to suppress bulk waves or to facilitate manufacture, a step or a groove is provided in the substrate end surface, and the upper end surface of the substrate end surface or the groove There is a structure having an inner surface as a reflection end face (see Japanese Patent Laid-Open Nos. 4-82315 and 7-263998). For example, in Japanese Patent Laid-Open No. 4-82315, the resonance of the SH wave is achieved by providing a step at a height position that is more than the thickness at which 80% of the SH wave energy is concentrated from the surface of the substrate. On the other hand, the influence of bulk wave resonance can be cut off, and unnecessary spurious based on bulk wave resonance is effectively suppressed.
[0003]
[Problems to be solved by the invention]
However, even when the height of the reflection end face is set to a predetermined height or more as described above, desired resonance characteristics and passband characteristics may not be obtained. That is, in a surface acoustic wave device in which a reflection end face is formed by steps or grooves as in the conventional case, even if the height of the reflection end face is set to an appropriate value, if the distance between the substrate end face and the reflection end face increases, the surface wave device passes. There were problems such as ripples in the band. Further, when the height of the reflection end face is increased, there is a problem that ripples are generated in the passband.
[0004]
SUMMARY OF THE INVENTION An object of the present invention is to provide a surface wave device that can reliably obtain desired resonance characteristics and passband characteristics by reducing ripples caused by bulk waves.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the present invention comprises a piezoelectric substrate and an IDT formed on the piezoelectric substrate, and a reflection end surface for reflecting surface waves on the upper surface side of the piezoelectric substrate outside the IDT. In the surface wave device provided with a groove or a step forming the surface wave device, the surface wave device is an end face reflection type longitudinally coupled resonator type filter, laterally coupled resonator type filter, ladder type filter , and the wavelength of the surface wave is λ The distance L between the end face of the piezoelectric substrate and the reflection end face is set to 8λ or less, and the height H of the reflection end face is set to 2λ to 4λ.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the present invention comprises a piezoelectric substrate and an IDT formed on the piezoelectric substrate, and a reflection end surface for reflecting surface waves on the upper surface side of the piezoelectric substrate outside the IDT. In the surface wave device provided with a groove or a step, the surface wave device is an end surface reflection type surface wave filter, and when the wavelength of the surface wave is λ, the end surface of the piezoelectric substrate and the reflection end surface The distance L is set to 8λ or less , and the height H of the reflection end face is set to 2λ to 4λ .
[0007]
The surface acoustic wave device in the present invention includes general devices using surface waves of SH waves such as surface acoustic wave resonators, longitudinally coupled resonator type filters, laterally coupled resonator type filters, ladder type filters, etc. One or more arbitrary numbers of interdigital transducers (IDT) are provided on a piezoelectric substrate, and a reflection end face for reflecting a surface wave is formed on at least one side of at least one IDT.
[0008]
The communication device according to the present invention includes a surface acoustic wave device having the above characteristics. Thereby, a communication apparatus with good characteristics can be obtained.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The configuration of the surface acoustic wave device according to the first embodiment of the present invention will be described with reference to FIGS. 1 is an external perspective view, and FIG. 2 is a cross-sectional view. In the following drawings, the width of the electrode finger of the IDT is shown as being wide, but in an actual product, the width of the electrode finger is very thin.
The surface acoustic wave device of this embodiment is an end face reflection type longitudinally coupled resonator surface acoustic wave filter, and includes a piezoelectric substrate 2 having a rectangular planar shape. The piezoelectric substrate 2 is made of, for example, piezoelectric ceramics such as lead zirconate titanate-based ceramics or piezoelectric single crystals such as LiNbO3 and LiTaO3. The piezoelectric substrate 2 has opposing end surfaces 21 and 22, and grooves 23 and 24 are formed in parallel with the both end surfaces 21 and 22 on the inner upper surface (one main surface) side of the both end surfaces 21 and 22, respectively. , 24 are configured so that the inner surfaces 23a, 24a function as reflection end surfaces for reflecting surface waves.
[0010]
Two IDTs 3 and 4 are formed between the grooves 23 and 24 on the upper surface of the piezoelectric substrate 2. The IDT 3 includes a pair of comb electrodes 3a and 3b. Each of the comb electrodes 3a and 3b has a plurality of electrode fingers, and the electrode fingers of the comb electrode 3a and the electrode fingers of the comb electrode 3b are inserted into each other. It is arranged to fit. Similarly, the IDT 4 includes a pair of comb electrodes 4a and 4b, and the comb electrodes 4a and 4b are configured similarly to the comb electrodes 3a and 3b. The electrode fingers are arranged in parallel with the grooves 23 and 24, and the outermost electrode fingers 3c and 4c of the IDTs 3 and 4 are arranged so that the outer edges thereof are in contact with the reflection end faces 23a and 24a. In this case, the outermost electrode fingers of the IDTs 3 and 4 have a width of approximately λ / 8, and the other electrode fingers have a width of approximately λ / 4.
[0011]
In this configuration, when an input voltage is applied to one IDT, the surface wave of the SH wave is excited, the excited surface wave propagates in the direction connecting the reflection end faces 23a and 24a, and is reflected by the end faces 23a and 24a. Further, the fundamental wave and the higher-order mode wave are combined, and a standing wave is generated between the end faces 23a and 24a. The output based on this standing wave is taken out by the other IDT and operates as a longitudinally coupled resonator type filter using the surface wave of the SH wave.
[0012]
In this surface acoustic wave device, each distance L from the reflection end faces 23a, 24a to the substrate end faces 21, 22 is formed to be 8λ or less. Further, the reflection end faces 23a and 24a, that is, the depths H of the grooves 23 and 24 are formed to be in the range of 2λ to 4λ.
[0013]
Next, FIG. 3 shows a configuration of a surface acoustic wave device according to the second embodiment of the present invention. In the surface acoustic wave device of this embodiment, a reflection end surface is formed by providing a step on a substrate end surface. That is, in this surface acoustic wave device, steps 25 and 26 are formed on the two opposing end surfaces 21 and 22 of the piezoelectric substrate 2, respectively. The steps 25 and 26 are formed so that the upper surface side of the piezoelectric substrate 2 is cut out in a rectangular shape, and the end surfaces 21a and 22a above the steps 25 and 26 are used as reflection end surfaces. The portions constituting the IDT other than the configurations of the reflection end faces 21a and 22a are the same as the configuration of the first embodiment, and the description thereof is omitted.
[0014]
In this surface wave device, each distance L from the reflection end faces 21a, 22a to the substrate end faces 21, 22 is formed to be 8λ or less, and the height of the reflection end faces 21a, 22a, that is, the piezoelectric substrate 2 of the steps 25, 26 is formed. The distance H from the upper surface is formed to be in the range of 2λ to 4λ.
[0015]
The surface acoustic wave devices of the first and second embodiments are manufactured as follows. First, a large number of IDTs constituting the surface wave device are formed on a piezoelectric mother substrate. Next, grooves (23 and 24 in FIGS. 1 and 2) for forming a reflection end face are formed on the upper surface side of the piezoelectric mother substrate using a dicer or the like. The groove is formed with high accuracy so that no chipping or the like occurs on the inner surface of the groove so that the outermost electrode fingers 3c and 4c of the IDT have a predetermined width. One side of the side surface of the groove is the reflection end face 21a, 22a, 23a, 24a, and the depth of the groove (the height of the reflection end face) is set in the range of 2λ to 4λ. Next, the outside of the groove or the inside of the groove is cut using a dicer or the like, and separated into individual surface wave devices. The cut surfaces at this time become the end surfaces 21 and 22 of the piezoelectric substrate 2, and the cut surfaces are set to 8λ or less from the inner surface of each groove. That is, if the outside of the groove is cut, the surface wave device of the first embodiment is obtained, and if the inside of the groove is cut, the surface wave device of the second embodiment is obtained, and a step is formed on the substrate end face. Thus, after forming the groove | channel which becomes a reflective end surface, the reflective end surface with high precision without chipping etc. is formed by cut | disconnecting the piezoelectric substrate 2 in a position different from a reflective end surface.
[0016]
Next, the reasons for limiting the distance L between the substrate end surface and the reflection end surface and the height H of the reflection end surface will be described based on experimental results. In such a surface wave device, the state before cutting and separation, that is, when the distance L is substantially infinite (actually when the distance L is 500λ or more), the bulk wave at the substrate end face Since no reflection occurs, ripple and insertion loss are minimized. Further, the in-band ripple in the insertion loss-frequency characteristic corresponds to the in-band GDT deviation, and the in-band ripple was evaluated by the GDT deviation.
FIG. 4 shows the relationship between the distance L after cutting and the amount of change in GDT deviation in the passband when the piezoelectric substrate is cut before, in the surface acoustic wave devices of the first and second embodiments. FIG. A filter for 1st IF of a mobile phone having a center frequency of 190 MHz and a passband width of 5 MHz, in which the total number of electrode fingers of IDT 3 and 4 is 34 pairs, the wavelength λ of the surface wave is 20 μm, and the height H of the reflection end face is 3λ. It is. As shown in FIG. 4, the in-band GDT deviation greatly changes when the distance L between the substrate end face and the reflecting end face is 8λ, the change in the GDT deviation is small when the distance L is 8λ or less, and the distance L is 8λ or more. The amount of change in GDT deviation is large. That is, if the distance L is set to 8λ or less, the ripple in the passband can be reduced.
[0017]
In order to prevent chipping or the like from occurring on the reflection end face, that is, to form a highly accurate reflection end face, a step is necessary, and the distance L is preferably set to λ / 10 or more.
[0018]
FIG. 5 is a diagram showing the relationship between the height H of the reflection end face, the in-band GDT deviation, and the minimum insertion loss in the surface acoustic wave device of the above embodiment. The data is when the distance L between the substrate end face and the reflection end face is λ. As shown in FIG. 5, the in-band GDT deviation is small when the reflection end face height H is in the range of 2λ to 4λ and is less than 0.125 μs, which is the use level, and when the reflection end face height H is less than 2λ. The surface wave energy cannot be reflected and the minimum insertion loss is large. That is, if the height H of the reflection end face is set in the range of 2λ to 4λ, the ripple in the passband and the insertion loss can be reduced, and good passband characteristics can be obtained.
[0019]
In the above embodiment, the configuration of the longitudinally coupled resonator type filter has been described as an example. However, the surface acoustic wave device may be a laterally coupled resonator type filter, a ladder type filter, or a surface acoustic wave resonator. Further, the reflection end face is not limited to the one formed on both sides of the IDT, and the reflection end face may be provided on one side of the IDT constituting the surface wave device and the reflector may be provided on the other side of the IDT. . For example, when a ladder type filter is configured by arranging a plurality of surface wave resonators on the same piezoelectric substrate, a configuration using end surface reflection by a reflection end surface and reflection by a reflector is employed.
[0020]
Next, the configuration of a communication device according to the third embodiment of the present invention is shown in FIG. In this communication apparatus, an antenna ANT is connected to an antenna end of a duplexer DPX including a transmission filter TX and a reception filter RX, a transmission circuit is connected to an input end of the transmission filter TX, and an output end of the reception filter RX. The receiver circuit is connected to the receiver. A transmission signal from the transmission circuit is transmitted from the antenna ANT through the transmission filter TX. A reception signal received by the antenna ANT is input to the reception circuit through the reception filter RX.
[0021]
Here, the surface acoustic wave device according to the present invention can be employed as the reception filter RX, the 1st IF filter of the reception circuit, the various interstage filters of the communication device, or the oscillation element. By using the surface acoustic wave device according to the present invention, a communication device having good characteristics can be obtained.
[0022]
【The invention's effect】
As described above, according to the surface acoustic wave device of the present invention, by setting the distance between the substrate end surface and the reflection end surface to 8λ or less, ripples in the passband caused by bulk waves can be reduced, Resonance characteristics or passband characteristics can be obtained. Furthermore, by setting the height of the reflection end face within a range of 2λ to 4λ, ripples in the passband can be reduced, and desired resonance characteristics or passband characteristics can be obtained.
[0023]
In addition, by mounting the surface acoustic wave device according to the present invention, a communication device having good characteristics can be obtained.
[Brief description of the drawings]
FIG. 1 is a perspective view of a surface acoustic wave device according to a first embodiment.
FIG. 2 is a cross-sectional view of the surface acoustic wave device according to the first embodiment.
FIG. 3 is a cross-sectional view of a surface acoustic wave device according to a second embodiment.
FIG. 4 is a diagram illustrating a relationship between a distance between a substrate end surface and a reflection end surface and an amount of change in an in-band GDT deviation.
FIG. 5 is a diagram showing the relationship between the height of a reflection end face and in-band characteristics (GDT deviation, insertion loss).
FIG. 6 is a block diagram of a communication device according to a third embodiment.
[Explanation of symbols]
2 Piezoelectric substrates 21 and 22 Substrate end surfaces 21a and 22a Reflective end surfaces 23 and 24 Grooves 23a and 24a Reflective end surfaces 3 and 4 IDT

Claims (4)

A surface acoustic wave device comprising: a piezoelectric substrate; and an IDT formed on the piezoelectric substrate, wherein a groove or a step forming a reflection end surface for reflecting a surface wave on the upper surface side of the piezoelectric substrate outside the IDT is provided. In
The surface acoustic wave device is an end face reflection type longitudinally coupled resonator type filter ,
When the wavelength of the surface wave is λ, the distance L between the end face of the piezoelectric substrate and the reflecting end face is set to 8λ or less, and the height H of the reflecting end face is set to 2λ to 4λ. Surface wave device. A surface acoustic wave device comprising: a piezoelectric substrate; and an IDT formed on the piezoelectric substrate, wherein a groove or a step forming a reflection end surface for reflecting a surface wave on the upper surface side of the piezoelectric substrate outside the IDT is provided. In
The surface acoustic wave device is an end face reflection type laterally coupled resonator type filter,
When the wavelength of the surface wave is λ, the distance L between the end face of the piezoelectric substrate and the reflecting end face is set to 8λ or less, and the height H of the reflecting end face is set to 2λ to 4λ. Surface wave device . A surface acoustic wave device comprising: a piezoelectric substrate; and an IDT formed on the piezoelectric substrate, wherein a groove or a step forming a reflection end surface for reflecting a surface wave on the upper surface side of the piezoelectric substrate outside the IDT is provided. In
The surface wave device is an end surface reflection type ladder filter,
When the wavelength of the surface wave is λ, the distance L between the end face of the piezoelectric substrate and the reflecting end face is set to 8λ or less, and the height H of the reflecting end face is set to 2λ to 4λ. Surface wave device . Communication apparatus characterized by comprising a surface acoustic wave device as claimed in claims 1 to 3.

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